Answer:
Holding additional capital will help avoid failure in the future by reducing solvency risk. During the 2007-2009 crisis, the market value of many assets held by banks was downgraded to garbage and became practically worthless. At the point the government had to intervene (with TARP) to save banks from collapsing.
Instead of cash, banks had huge reserves of financial assets that were worthless, which meant that they had very little to pay their clients when they would try get their money out. The only way to reduce the solvency risk (bank not being able to meet cash obligations) is to hold more cash and increase capital.